1. Field of the Invention
The present invention relates to a processing apparatus and a processing method, more specifically to a processing apparatus including an invertible collimator optimum for titanium sputtering or reactive sputtering of titanium nitride, and a method using the processing apparatus.
2. Description of the Prior Art
A semiconductor device fabrication process conventionally uses a sputtering system to form electrodes on objects to be processed, such as semiconductor wafers, and to wire the objects. The objects are positioned opposed to a target of a required film forming material in a processing chamber the interior of which is kept in a required low pressure atmosphere, whereby particles sputtered from the target are applied to the objects.
Accompanying the recent high density integration of semiconductor devices, techniques for accurate micron sized processing during their fabrication processes are required to be developed. In internal wiring processing using sputtering systems, for example, it is necessary to fill contact holes having small diameters and large depths, i.e., high aspect ratios, with sputtered particles. But generally the known sputtering processes have low step coverage characteristics, and as the cavities of the contact holes have larger aspect ratios, wiring discontinuities tend to occur at the bottom of the holes. This is a problem of the conventional technology.
As a countermeasure to this problem there has been recently used a sputtering system including a collimator 5 which comprises, as shown in FIGS. 10 and 11, a plurality of circular through-holes 5a or a honeycomb of through-holes FIG. formed through a metal plate of, e.g., steel, or an insulating plate made of ceramic. The collimator 5 is positioned between a target and objects to be processed to restrict the directions of travel of the sputtered particles in a cos .theta. distribution from the target so that only selected particles substantially perpendicularly bombard the surfaces of the objects to be processed, whereby improved step coverage is obtained. By the use of such collimator, a step coverage is obtained which is improved by about three times the usual step coverage for contact holes of aspect ratios of above 3.0 which are required in the fabrication of, e.g., 64M DRAMs.
But collimators used in sputtering systems for the improvement of step coverage sometimes cause large amounts of particles, depending on materials of the collimators, to be formed. For example, in forming an ohmic contact layer between an electrode/wiring material, and silicon, as shown in FIG. 12, a titanium film 73 as a contact layer is formed on a silicon substrate 70, and a titanium nitride film 74 is formed as a barrier layer for prevention of reaction between the electrode/wiring material and the silicon, and as an adhesion layer, when the electrode/wiring material is CVD tungsten 75. But a problem is that titanium nitride, which is stable and hard to react, has poor adhesion and more easily peels than titanium, causing particles to be formed.
Titanium nitride is generally sputtered by reactive sputtering, because titanium nitride as a target material is not commercially available. In this reactive sputtering, discharge is conducted with argon and nitrogen gases, which are usual sputtering gases, being introduced into a processing chamber at required flow rates to nitrify the titanium near the surface of the target or the surfaces of the wafers to form titanium nitride films. But because titanium, which is unstable and active, tends to be contaminated by a residue of the gases in vacuum, titanium sputtering and titanium nitride reactive sputtering cannot be conducted by using one and the same titanium target. Accordingly, the sputtering and the reactive sputtering must be conducted in different processing chambers, or the surface of the target must be cleaned before the titanium sputtering, which has been a serious barrier to improvement of productivity.